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GAMMA-RAY BURSTS AND MAGNETARS

Yun -Wei YU 俞云伟 June 22, 2010, Hong Kong. GAMMA-RAY BURSTS AND MAGNETARS. Outline. Background Implications from the shallow decay afterglows of GRBs A qualitative discussion on magnetar wind emission Emission from the termination shock of the wind. 1 Background.

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GAMMA-RAY BURSTS AND MAGNETARS

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  1. Yun-Wei YU 俞云伟 June 22, 2010, Hong Kong GAMMA-RAY BURSTS AND MAGNETARS

  2. Outline • Background • Implications from the shallow decay afterglows of GRBs • A qualitative discussion on magnetar wind emission • Emission from the termination shock of the wind

  3. 1 Background

  4. The basic properties of GRBs Spectrum Light curve

  5. Two possible progenitors What is the remnant central compact object? Black Hole or Neutron Star?

  6. F Afterglow Emission Fireball model t Prompt Emission

  7. 1997: The detection of afterglow emission from GRB970228 BeppoSAX X－ray optical

  8. November 20th, 2004, Swift satellite was launched, where three instruments on board including BAT, XRT, and UVOT.

  9. The main achievements of Swift • Uncovered many detailed features of the X-ray afterglow light curves • Multi wavelength observations for the prompt emission • Detected very high-redshift GRBs • Discovered the afterglow emission of short GRBs and thus their host galaxies • ……

  10. 2, The shallow decay afterglows and millisecond magnetars

  11. Two problems: • Why the early light curve is much flatter than the one predicted by the standard model? • How can the sharp flares occurred during the afterglow phase? Standard model F F t t

  12. A very probable answer:The GRB central objects have long-lasting activities after the burst phase. e.g., Yu & Dai (2009)

  13. Millisecond magnetars Millisecond magnetars could be plausible candidates Several models have been proposed to describe how a millisecond magntar can driven a GRB

  14. A natural consideration: Energy injection GRB ejecta and shocked medium Surrounding medium Magnetar The spin-down energy of the magnetarcould be absorbed by the GRB blast wave —— The shallow-decaying afterglow Dai & Lu (1998) GRB external shock

  15. Emission from an energized shock

  16. 3, A qualitative discussion on wind emission

  17. Supernova ejecta Pulsar wind

  18. Can the wind produce emission directly? GRB ejecta and shocked medium Surrounding medium Magnetar Two Emitting Regions: The GRB Shock and The magnetar Wind GRB external shock

  19. The spin-down of a magnetar Yu, Cao, & Zheng (2009)

  20. The spin-down of a magnetar Yu, Cheng, & Cao (2010)

  21. Emission from an energized shock

  22. Shock Emission? Wind Emission?

  23. Implications to the properties of magnetars

  24. 4, the termination shock of the magnetar wind

  25. Wind termination shock GRB external shock Yu & Dai (2007) 3 1 4 2 Shocked wind Unshocked wind Shocked medium Unshocked medium

  26. Yu & Dai (2007) Mao, Yu, Dai et al. (2010)

  27. Conclusions • The central objects of SOME gamma-ray bursts could be millisecond magnetars. • Some x-ray afterglow emission could be directly produced by magnetar winds, rather than the external shock. • We may be able to derive the properties of some newly born magnetars from some observational GRB afterglow data. • More careful calculations are needed.

  28. Thank you!

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